1. Field of the Invention
The present invention relates to a method of fabricating a catalyst converter for purifying exhaust gases.
2. Description of the Related Art
As for this type of catalyst converter, it is conventionally known that diffuser portions of a cylinder portion of the catalyst converter are formed by plastic processing based on spinning.
FIG. 3 shows one example of the above catalyst converter.
First, a metallic plate member 1 of a rectangular shape is prepared. Next, this plate member 1 is rolled up, and its both ends la are caused to abut against each other and are subjected to welding such as tungsten inert gas welding (TIG) or metal inert gas arc welding (MIG).
Next, a catalyst carrier 3 is pres fitted into a tubular member 2 thus formed.
Next, drawing based on spinning is effected for both end portions 2a and 2b of the tubular member 2 with the catalyst carrier 3 incorporated therein.
Next, a pair of flanges 4 are attached to opposite ends of the both end portions 2a and 2b of the tubular member 2 subjected to drawing.
A catalyst converter 5 can be obtained in the above-described manner.
According to the conventional fabrication method, however, when after the plate member 1 is rolled up, both ends 1a are caused to abut against each other and are subjected to welding such as TIG or MIG, as shown in FIG. 4, burn through occurs at a starting point and a terminating point of welding of the plate member 1, and if drawing based on spinning is effected for the both end portions 2a and 2b of the tubular member 2, cracks 7 can possibly occur at its burn through portions 6, as shown in FIG. 5.
The invention has been devised to overcome the above-described problems, and its object is to provide a method of fabricating a catalyst converter which makes it possible to prevent the burn through in the plate member during the formation of the tubular member.
To achieve the above object, according to the present invention, there is provided a method of fabricating a catalyst converter comprising the steps of: obtaining a tubular member by rolling up a metallic plate member of a rectangular shape having ear portions at four corners thereof such that opposing ones of the ear portions abut against each other, and by effecting butt welding for both ends of the plate member; cutting off projecting portions formed by the ear portions at both ends of a weld of the tubular member; incorporating a catalyst carrier into the tubular member with the projecting portions cut off; effecting drawing for both end portions of the tubular member with the catalyst carrier incorporated therein; and attaching a pair of flanges, respectively, to the both end portions of the tubular member subjected to drawing.
Also, according to the present invention, in the method of fabricating a catalyst converter, each of the projecting portions formed by the ear portions may have a substantially trapezoidal shape, and an amount of projection thereof is longer than a burn through portion formed in butt welding.